He Gained A Lot Of Weight

So my bf and I have been together for about 5 years now. I love him with all my heart and we are planning on getting married once I graduate college. That being said, as of recently our sex life has been dwindling and I’m finding it extremely difficult to come up with a solution. Firstly let me acknowledge that this issue in the bedroom is 100% my issue and my problem, I do not blame my bf for any of it. About a year and a half ago my bf steadily put on over 60+ lbs putting him close to 230lbs...which was initially fine with me (I don’t judge I fell in love with his heart and personality first). However as of these recent past few months, I have found it extremely difficult to get aroused when we are together. I am way shorter and smaller than him so having sex can sometimes be a extremely labor-some activity. I have found myself staring at slimmer men and unconsciously having thoughts about what they are like in bed. And when I catch myself doing that, I cry, every time. Of course I love my boyfriend but this issue has really made our sex life rocky and I need some advice please help...

***as a note I again want to make it clear that I still am head over heels for him. And I want to acknowledge that I am not SUPER fit myself, I’m slim but still have some fat on my stomach and arms. I’m not expecting or wanting a Zac Efron, I just miss and feel more attracted to the way he looked in the beginning of college... please don’t come at me I really do love him this issue is just difficult to resolve***