Is it normal that my girlfriend makes me cum in a tissue and keeps it?

She probably tries to impregnate herself with it

I don't see a problem with it. Like a lot of guys, I get turned on by my wife's panties. She's a bit embarrassed about it, though, so I don't press the issue. But if she let me, I'd keep a pair of her (worn) underwear under my pillow when she's out of town.

And some people are just really turned on by semen. If she likes it, maybe let her go for it. You should be flattered!

It would be more appealing if it was underwear or something for at home. Not a piece of trash in her pocket.

Tell her that is a very stupid thing to do.

What she's doing is unusual, but what's even more unusual - in a positive way - is that she feels free to be honest with you about what she's doing.

Humans tend to be primarily visually-oriented, but we have nearly as many olfactory nerve endings in our noses as dogs. Aromas affect all of us, but it's usually at a subconscious level. However, some people are very olfactory-orientated, and smells are more important to them than they are for most people. That makes them different, not weird. Do you also find it disgusting how some guys sniff their sexual partner's underwear when they're masturbating? If you find the idea of doing that twisted or perverted or something, this says a lot more about you than it does about them.

Frankly, you sound like a prude with very little experience of life and someone whose beliefs about what's acceptable are rooted in whatever flavour of sex-negative brainwashing you were subjected to as a kid. Your strong reaction to what she's done also suggests that you find your own semen disgusting or unclean. If you don't want to enjoy sex as much as you can, dump the girl and stay stuck in your comfortable little box. If you'd like to expand your horizons and join the real world, stick with the girl and learn how to be more open to new experiences and more accepting of how people are different.

What she's doing doesn't have any real impact on you. I suggest that you need to learn how to accept that people have the right to do whatever the hell they want as long as it doesn't harm anyone else. I think you also should try to accept that people won't always conform to whatever your narrow concept of 'normal' is, and to recognise that those who insist on staying vanilla because they feel that's what 'everybody' expects of them become very boring, very fast.

What your girlfriend is doing is degenerate, and creepy as Hell. If I were in your shoes I would dump her. When you eventually come to your senses, and dump this chick don't be surprised if she stalks you.