cat that wont use litter box

hello i have a male kitty who is almost a year old for some reason he will not use his litter box all the time. most of the time he will find some where on the floor to go potty.
we have two cats. he is fixed, and then we have a female kitty who is not fixed. we have two separate litter boxes. we also have a male dog.
when we first got our dog i think it threw my male cat off because we where having the same issue but he finally came around and tarted using his litter box again, but we just went on a 5 day vacation with family members watching over them while we where gone he did not use litter box and since we have been home he hasn't used it.
im just trying to figure out if anyone knows why or what i could do to help him start using it again.
thank you.

A few ideas:
First, he needs to go to the vet to rule out a uti or something physical.

Second, it could be related to stress. The female cat being in heat could be be a trigger, as is you going away. Do you plan to get her spayed? The hormones are stressful for both of them.

How many litter boxes do you have? How often do you clean them?

hello thank you!

yes i do plan on getting her spayed i have 2 litter boxes and i scoop every day.

he has been very needy lately. like he is always very sweet but he wont leave me alone he just wants so much attention

Ok, so first step definitely needs to be a vet visit. You could also try adding a third box. You also need to use an enzyme cleaner anywhere that he has gone outside the box.

Have you tried anything to calm him down, like a feliway diffuser or composure treats?

no i haven't where can i get those from?

You can probably buy either on Amazon.com. Also pet stores would carry them.