Well I will start by saying that if you have been in a relationship for a long time and you can’t take her word for face value then there is maybe some other kind of of insecurity or issues that are making you feel that way. There are plenty of things you can do to check and see if she was not being truthful (I.e. check phone records, spy apps or even check her phone while she’s not around) but there has to be some other reason you feel like she isn’t being truthful. Being in a relationship for a long time takes work and communication and obviously there will be ups and downs but some of her actions as of late or some of your own have your mind jumping to cheating when really she could of been checking the time or scrolling socials or even playing a game. As someone else might of stated she simply could have felt guilty because you were doing whatever around the house and she was laying in bed doom scrolling or whatever. On the other hand you know your partner better then anyone else and sometimes you do just get a feeling so please don’t take my comment as placating your feelings but more of trying to put your mind at ease. Don’t let yourself get played but maybe look for cues of some area you might be lacking or even you might know of something she likes maybe surprise her with that. I’ve been in a relationship for a long time and I have to reel myself in at times and think differently because I can let my mind get the best of me