Is this sighns of cheating?

ok so my mom and dad are married. and 1 day my moms phone said 1 new message from "steve". that's not my dads name so i was Curious. so when my mom was out and forgot her phone it said i want you to nurse me. 0-o. and apparently my mom was sending naughty pics to him. 0-o. and when she went "out" she was really over at Steve's house taking pictures of you know what. and i really don't think my dad knows who steve is and i don't know if there having sex or what but please help? could she be cheating?