Look. People sometimes post things that are obvious. Eg. that they don’t like the pew color so they don’t want to go to Mass. Baring any mental illness, it woul be a mortal sin.
I think that missing Mass is sometimes, many times, a mortal sin. People get lazy and choose to shut off their relationship to God. It isn’t always mortal-as in competely cuts off our relationship to God. Some posters use hyperoble to point that out. As for myself, I think that Mass is truly a treasure and going is gift from God. God, come down to serve us in Holy Communion…and we get to be there…AMAZING. But not every reason that negats mortal sin for missing mass has to be life or death. Sometimes its just life. We must be careful to not make a habit of it. But it happens. Is willfully and hatefully missing mass a mortal sin? Yep. But that’s becuase it purposfully rejects God and your relationship with God. Will the punishment be as bad as that of a murder? No. But cut off from God is still cut of…and it’s not a good place to be.
This forum has a tendency to deamonize those posters who get in particular situations that they may not be in control of. There are threads where posters say it is better to be abused or killed for no reason than to lie…about anything…even a broken pencil. There are threads that condem people for reading certian books and equate it to devil worship. There are threads that condem people for wearing jeans to Mass to the same disrespect as if they were spitting at the priest.
Look around. It can be a nasty place to be.
Only the OP and the priest can decide if this is a mortal sin or not. Certinally it his indicision and then not going when he has other means (car, etc) can be a minor sin, but we don’t know his relationship with his parents, church or world that might mean he’s completely sinless in this.