Why would my girlfriend stop me halfway into our makeout session and say "not tonight"?

Anonymous
My girlfriend and I went out to dinner and then drinks last night.

We called it a night around 11 and I dropped her to her house after. She told me she really wanted me to come in so I did.

After a couple minutes of watching TV on the couch, we started kissing, something she initated and then it got hot and heavy.

I got on top of her and started feeling her up outside of her shirt. Mean while she started kissing me even harder.

After a couple more minutes, I started taking off her shirt, but she immediately stopped me and told me “not tonight”, and if it was OK if we just cuddle tonight.

I really love her, and really do just like spending time with her so I agreed and we just cuddled for the rest of the night.

I really don’t mind cuddling, but I was really annoyed at her for stopping me last night. I mean if she just wanted to cuddle for the night she should have said so from the beginning right?

Instead she tells me to come in, initiates the kiss, let’s me feel her up, and gets me hot and hard only to stop me midway.

Ladies, can you explain this behavior to me?

Updates
+1 y
-We've been dating for 5 months.

-She's stopped me once before, saying she was tired and not in the mood as well, but she made it clear before we started kissing.

Why would my girlfriend stop me halfway into our makeout session and say "not tonight"?
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