How come all of my relationships last no more than a couple of months?

I've been online dating for about 4 years and I recently got out of a relationship with a girl I met on a dating app.

We dated for almost 2 months until she broke up with me a few days ago because she said she didnt feel any "chemistry" with me.

The last relationship I had before her only lasted one month. The guy was a very conservative Christian and when he found out I was bisexual, we went our separate ways because he could neither accept nor understand my queerness.

All of the people I met either end up telling me they're not interested after the first date or we go out for a few dates before they move on to someone else.

Is there something wrong with me? Am I just THAT effing ugly. Honestly, I'm overweight and have acne but I've seen people who have these same weight/skin problems but they're in happy relationships.

My brother has been with his girlfriend since 2018 and it makes me wonder why my relationships cannot last that long. He is younger than me too, which makes me feel worse.

When I fall for someone, I fall really hard. I make playlists filled with songs that remind me of that person, buy them gifts, write poems/journal entries, etc.

I even wrote a letter for my most recent ex (the girl) that I was going to give to her on valentines day but that is obviously not going to work out anymore. It included this:

"I feel so comfortable around you. I can honestly say I'm the happiest I've ever been since you came into my life."

My mom tells me I should stop looking for happiness in other people, however. I wouldn't say I'm unhappy (although I do take antidepressants) but being with her made me happy. So it just kind of sucks. However, I did not cry over the breakup which surprised me. My work and my schooling has been affected though. I feel like I'm mourning someone and need time for myself because of this whole breakup situation.

I just do not understand why I can't keep anyone interested in me. I have friends that have stuck around for years but partners only last me a couple of months or less. I do not know what to do.

Anyone have any input?