advice ?

Recently my boyfriend keeps saying no and not wanting to sext anymore. then this guy friend of mine wanted me to start sexting with him last night and i did. It went on for almost 3 hours. I feel so bad about it, i love my boyfriend i really do, i love him more than i can explain. And knowing that i did this to him in my moment of weakness is killing me. Did i really cheat ? Should i tell him ?