I can relate to a lot of your concerns. My wife and I were both virgins at marriage. I don't know what the bases are these days. I don't think I ever did, but I hear they have changed-- gotten more extreme over time. Before marriage, I kissed my wife and was probably overly affectionate in certain ways. I never grabbed her breasts so I don't know if I went to any of the bases except first? (is kissing first base)? We were virgins at marriage, but hadn't given each other 'release' before our wedding night. Early on, she kept up with my drive one way or another. It's been up and down a bit since then, especially with childbirth related issues. That's normal. You aren't going to get consistent 'release' during all the stages of the month and childbirth and you shouldn't expect to. And as you age, if you don't have it as often as you like, it doesn't cause the difficulty sleeping it can in your 20's.
Should you call it off? Wow. My concern with getting engaged was that in the Bible-- in the Old Testament-- the only part that deals with certain of how to get engaged and married at least in regard to God's commandments for Israel-- once a man is betrothed to a woman, he has to divorce her to break it off. It's not just an easy light thing. And my mindset, after reading the words of Christ and Paul, was to never get divorced. If I were in that situation now, I'd treat it the same way-- except after I got her father's consent, I'd consider it to be a done deal as far as I was concerned not as far as having a wedding night early or anything like that, but as far as not breaking it off and considering us to be under an indissoluable bond. That's the way I look at it, erring, if I am, on the side of caution, since you can also argue that in our culture the father does not give the bride away until the wedding.
If it were a dating situation and I were in your shoes--and we were both sexually pure-- but somehow I knew she'd want sex once a month, and I had your needs, I would seriously consider breaking up over it. If we were engaged, and hadn't sunk money into it, I might consider delaying the wedding until we worked through the issue. But if you've got invitations out there and you've promised to marry her and gotten consent from parents, I can't in good conscience encourage you to back out. Add to that the fact that you have gone to all these bases with her, and taken something of her purity that you can't give back. I don't think in your situation it would be fair to her to reject her.
If you got feverish over lack of sex, the chance of meeting someone with the same sex drive as yourself who is also a Christian, who you also like who you click with is unlikely. Fariness and feelings aside, if you were to go back 'on the market' how long would you have to go without sex before you found someone who meets your non-sexual criteria who you could convince to marry you? That's a long process. Finding someone who meets your sexual criteria on top of that could add more time to it.
Your fiancee's thinking on this needs to change, and it needs to change by her submitting herself to the word of God. Her sister is her sister and you have to respect that, but it sounds like she is not a good role model. You need to get the idea to her, gently without insulting her sister, that her sister has some issues. She's got a problem when it comes to sex. Once a month is below average. Two to three times a week, I think, is more realistic, and nowadays consider the population bubble with the seniors in the US population. Two times a week includes all those senior citizens and all the people with health problems not including age. It's likely that young couples are more active-- especially newly weds. It's normal to have a lot of sex early on.
Your fiancee needs to have some godly voices speaking into her wife. It sounds like her sister is not someone she should be listening to about this. I'm also wondering, why should she be telling her sister about your sexual needs? I know girls talk about such things, but I can talk to my brother, but I can't see myself going into great detail about something personal about my wife like that. Maybe if it were really bothering me.
I'd talk to my fiancee if I were you about marriage and divorce in scripture, pointing out that betrothral in scripture required divorce. I'd also talk to her out of I Corinthians 7, which tells you both to meet one another's sexual needs. It's good to enter marriage with a commitment from both ends on this matter. You could point out that the tables may turn as you age and she reaches her 'peak' (if that is not just a myth) and you get older. Of course, you can wait until you are married (after you are sure she has had an opportunity for some enjoyable intimate time together) to study I Corinthians 7 and both agree to follow it.
You should also think a little more deeply about what you want in marriage. I loved my wife when we married, but the main need I wanted her to meet-- besides the emotional need I had to be around her and see her every day, hold her, etc.-- was sexual. I didn't care if she cooked, cleaned, and I didn't think that much about kids at first. But now having been married to a diligent woman and having gone through some ups and downs of marriage, I know what I want in a wife. I want a woman who loves the Lord, who is diligent with housework and cooking, who prays and intercedes with the Lord. I want a woman who knows how to take care of children. I also want a woman who respects me and submits to me-- because this is the will of God-- who also takes my sexual needs seriously. Of course, I want a woman who loves me. It's a real blessing to have a woman of God like this for my wife.
Early in marriage, I'd be focusing in with her in prayer and Bible study on the role of husband and wife in the marriage. Part of that is sexual responsibilities towards one's mate. You can do a little of this now. "If I'm not in the mood, it isn't going to happen" is definitely the wrong attitude. The Biblical attitude is 'You have power over my body" and if one needs help getting in the mood the other is willing to help. Self-sacrifice as a husband may mean putting down your desire to have sex so your wife can sleep or pray when life gets busier.
I haven't read the whole thing, but the two volumes, "The Excellent Wife" and "The Exemplary Husband" may be good reads for some of these issues. You can read and discuss together. I'd like to do this with my wife if things calm down a bit and we have some free time at night. You might also look through this lady's videos for some things to recommend to your fiancee to walk. She does videos directed at wives. I haven't watched this one, but the ones I looked through looked very good. There are some sermons on YouTube directed toward men, but I haven't seen any vloggers doing the same sort of detailed teaching for men as she is doing for women. If your wife really liked these videos and listened, it might help her thinking. It's best to have real-life people around her. She needs people speaking into her life besides her sister. Here is the link to one of her videos
Are You Controlling Your Husband?Week Sixteen. - YouTube