I think your partner is being insensitive to you as a partner by pushing issues with which you are obviously uncomfortable.
You need to have a talk with him away from the bedroom.
Explain to him that you love him dearly, but that does not extend to actions with which you are uncomfortable - and you don't need to explain or justify why you feel this way, it is simply enough that you do.
Tell him that pressurising you only makes you feel more unhappy, and less able to comply, and that you need his understanding and support in not pressing you for his own pleasure.
If this conversation doesn't resolve the problem, I would think seriously about your long-term future with this man.
Any partner who is pressing his lover for aspects of inticimacy with which she is uncomfortable - and allowing her to feel guilty as a form of emotional blackmail, is not the sort of man who is going to provide the basis of a long-term commitment.
If he is selfish in bed, he will soon become selfish out of it.
Have the talk, see how he responds, and move forward - which every way it takes you.
I do hope it works out for you.