Suspect cheating

My husband and I have been married 15 years and have 2 kids together. He was recently away for work for 6 months (military). Nothing crazy happened and throughout it I thought we maintained a good relationship. I would send him sexy pics and we would talk every day. He has been home for about 3 weeks now and the first 2 weeks were again normal nothing seemed out of place but now he’s acting funny.

He keeps his eyes glued to his phone, and his whole attitude changed and he seems distant. His phone is like glued to him he even has it under his pillow when he sleeps. I keep asking what’s wrong and he just says nothing and either changes the subject or walks away. I just have a weird feeling and I can’t shake it. I’m not one to check his phone (just never felt I needed to) and he always has it so I couldn’t even check it if I wanted to. Maybe I’m crazy. He has gone on a lot of military trips before and this is the first time I’ve gotten this sinking feeling. Would I be out of line to ask him straight out if it’s someone else ? I don’t have any proof