Right on, go with that pain in your gut. It's telling you what your conflicted thoughts can't.
Here's some encouraging truth from God's Word:
In 1 Corinthians 13, Paul categorizes Agape, the self-giving, other-directed love that is based on God's own nature (1 John 4:8):
4 Love is patient and kind; love does not envy or boast; it is not arrogant
5 or rude. It does not insist on its own way; it is not irritable or resentful;
6 it does not rejoice at wrongdoing, but rejoices with the truth.
7 Love bears all things, believes all things, hopes all things, endures all things.
It sounds like your boyfriend is not exhibiting this kind of love.
In Galatians 5 Paul compares the works of the flesh (corrupted desires) with the fruit of the Spirit:
17 For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for these are opposed to each other, to keep you from doing the things you want to do. 18 But if you are led by the Spirit, you are not under the law.
19 Now the works of the flesh are evident: sexual immorality, impurity, sensuality,
20 idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions,
21 envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God.
22 But the fruit of the Spirit is love, joy, peace, patience,kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law.
24 And those who belong to Christ Jesus have crucified the flesh with its passions and desires.
From your description, this man is choosing to oppose the Spirit of God and attempting to entice you to participate in sexual immorality, while not exhibiting evidence of the Spirit's presence in his live (self- control) and refusing to demonstrate his allegiance to Jesus by putting to death his passions, using them instead as his standard of happiness.
I have daughters; I would tell them this man doesn't have your best interest at heart. He wants to please himself. Compare that with the love of the Father in the Son who humbly became a servant out of love, and tasted death so we wouldn't have to.
Sexual expression in marriage is designed to be a joyful, pleasurable mutual celebration of faithful self-giving love; without a covenant commitment it is destructive and empty.