Why would my boyfriend ask for my underwear?

Answer :-

Opinion 1:-

I think boyfriend or girlfriend are the things that happens in early age, mostly it happens when peoples become adult and they feel the need of some apposite gender and then this happens some becomes boyfriend and some become girlfriend, and some still alone like me.

So i am going to giving you the exact reason after my earliest clarification.

And the and answer is" your boyfriend ask for your underwear because he is your boyfriend dear" answer already is in your question. It's depends in what manner your relation is going how you both takes each other in daily life.
And dont mind as i clarify the things before exact answer.

Opinion 2:-

There may be many reasons. Let me give you aquantance with some of them,

1. He want to put it under his pillow and when he ll be going for sleep he can feel the memories of your last sex.

2. He may b testifying you.
    How much trust do you have on him.

3. Yes, some people are addicated to the smell , this may be one of the reason.

4. Some people have unique tendency that they collect some special kind of things as a memory of their past relation
Example: penty, cap, hair samples,

5. Some people wore ( occasionally) the undergarments of their gf/bf.

6. He can blackmail you after break up that he is having your personal thing, you will be in shame after he showcase it

Now it depends on your relation and trust either to give or not.

Opinion 3:-

He might want them for whatever reason, as many of the men here say, but the truth is, you won't know until you ask. Being a woman and being very protective of myself and my things, I would want to know. You always need to keep it in the back of your mind that if things would ever happen to go bad between the two of you, he could (not saying he would) use them against you. The same way some boyfriends want naked or provocative pictures of us, and then if we get into a fight or break up, they send those pictures all over kingdom come. Or, the same way some boyfriends want our panties or one of our bras, we trust them, then they take pictures of them and send it to all of their buddies. I am not saying your boyfriend would do these things, but there are always possibilities. Just like some guys wanting them for under pillows and such. Those are the sweet guys out there and I'm sure your boyfriend is sweet and trustworthy. I'm generally a cynic, so take my view for what you will.
source:-quora.com