That's not "just crying sometimes", though, is it?
What I mean is, it's not random unprompted tears.
It's entirely justified, totally understandable tears, where a well-crafted piece of drama, with carefully-portrayed relationships embodying certain universally-understood tropes and archetypes, and skillful portrayals of relatable situations and powerful emotions, has connected with you and where you are in life right now, in just the kind of ways that drama is often intended to — your memories, regrets, hopes, fears, relationships, losses, and so on. Unfortunately, the places where it has connected with you are places which are very painful to the touch at the moment.
Not everyone will react in the same way to the same films, but when there are certain tender areas in your psyche, things which are written with the aim of connecting with people on an emotional level will probably provoke painful feelings if they probe at those areas.
It's an awful feeling, being so lonely when you're not technically alone, when you're with the person our culture constantly tells us is supposed to be the one who completes us, the one we can be ourselves with and feel a bond with like no other. That kind of loneliness that's actually accentuated, not relieved, by the presence of other people, and even more so when the other person is your partner.
Your tears aren't random outbursts — they're a real, sane response to something that's jabbing at a painful spot.
Edit to add: I'm not sure my tone is coming across how I intend here.
I'm trying to emphasise that you're not being irrational, you're not necessarily suffering from a clinical mental health problem (though I guess you may be, but I mean that you wouldn't have to be in order to have this kind of reaction to things), and your crying is not insignificant or unimportant or disproportionate. Even the most formulaic rom-com can make use of decades'-worth of techniques for connecting to the viewers' own emotions, and has many skilled people involved in carrying it out. So even something quite ordinary and clichéd can connect with authentic parts of us, and cause authentic pain when it does.