What should i do about my daughter?

i am a 39 year old married women. i have 4 kids my son is 1.5 yearsnmy daughters are 2 monts, 3 years and 17 years. my eldest daughter has been dating this guy since she was 15. she wants to sleep with him.she is a very responsible girl for her age as she will helo me with the chores,cooking and the kids without being asked.her boyfriend is a mature young thing.he is also 17.i dont want her not to sleep over but i also worry not about coz she isnt ready and she told me that herself . anyway back to the point. lately she has been getting really bad cramps while she is on her period. her boyfriend knows about this and has suprisingly to me has been very supportive and understanding.she is on her period just now and only started 2 days ago.what if she gets a cramp over there and cant come home? i dont want answers that say dont let her go she is gong to have . dont bother even replying coz i wont read it. please help me i am really stuck