Oxygen passes into the blood through tiny blood vessels called .(science*)

Capillaries

Explanation:

Deep within your lungs, this oxygen passes into your bloodstream through tiny blood vessels called capillaries. Oxygen-rich blood reaches your brain through your internal carotid arteries and your vertebral arteries.

if your boyfriend is cheating on you, my best advice to you is to dump him, he's only going to drag you down. and if you do, don't fret there's plenty better that know how to treat a person right. i mean honestly, the whole point of a romantic relationship is love, and if you love someone you aren't going to cheat on them. i do believe in second chances, but why would he cheat in the first place? i personally feel that if someone cheats, they ruin any chance they wanted/had with you. i wish you the best of luck with this, hang in there.