It's nota big deal, but can't get my head around what occurred last night.

I am at a bar and this cute, well dressed blonde girl (BG) comes in with her hipster, but well maintained girlfriend.

A guy friend of their shows up and joins their conversation. This guy is is a short (same as me), heavy set (not like me), but well dressed (not as well as me), but overall has a fairly boring look. This is Tweedle Dee.

BG begins to lean onto my chair while conversing with the above mentioned cast. Perfect opportunity to open her! I turn around start flirting: "Am I going to have to fight you for the back of my chair?" BG is very receptive and we flirt back and forth. Mostly negotiations on how much of my chair she is allowed to utilize. (Here was a good opportunity to make her buy me a drink, but it wouldn't have changed this particular outcome)

After a few moments I turn away from her to begin chatting up her friends. I chat up hipster girlfriend for a bit -we hit it off and become Facebook friends. She has a BF near by. I chat up Tweedle Dee for a bit - we hit it off well. Then back to BG.

With BG approx. 80% of the conversation is humorous flirty talk, 20% typical getting-to-know-you stuff. Poking fun at her jacket, her job...fun stuff. Personally, I'm proud at how god damn On I was with her, and I chalk that up to her receptive, fun, feminine personalty. (sidenote: I'm of the belief that attractive, feminine women really bring out the best in men; like cheerleaders. This is why frumpy, UGG wearing bitches are so devastating to society's psyche.)

Anyway, BG and I are talking and it's going very well. A good song comes on and I suggest we dance. It is not the type of place that people generally dance, but I always get it moving. I grab her hand and led her to the "dancefloor". Once there she is reluctant and says something about a girl she grew up with being there so she didn't; want o feel embarrassed.

I smelled bullshit and pushed the issue, grabbing her and spinning, a litte bit but she did not relent. Back to the bar, talked to Tweedle Dee & hipster friend....talked to other people at the bar...blah blah, blah.

Next thing I know she's making out with Tweedel Dee. OK, I get it, she had this plan in her head all along, there's really no fighting it. AH! but here is where I get lost.

I go about my business and about 30 minutes later BG is making out with some other dude. An even heavier, boring looking shlub! Tweedle Dum(b) for sure.

At this point Tweedle Dee rolls up to me and pathetically slurs, "Don't ever fall in love, bro." Poor guy.

Now, I understand that without serious A+ game I couldn't get her away from Tweedle Dee (right?), but what the hell happened that she ditched him for an even more dumpy, gross Tweedle Dum?

TL;DR Hit it off with a cute blonde girl, she makes out with her fat guy friend, then ditches him for a worse looking dude. Baffled by this.

Any similar experiences? Could I have done something differently??

EDIT: added detail