I have a question in my mind and it's what happens if i take a rest for maybe three months and i lose some muscles then i back to trainning again , does this affects my overall gains or is it harder to gain the muscles i lost ..

i took a month rest before and when i back i felt like things isn't as it was before ..

I know as time is passing while you train your gains decreases gradually , but i would like to know what happens when returning after long rest ..?

It depends how long you have been training before you take that long break. If you have been training for years, then with muscle memory, you would (likely) get back your gains faster than if you had only been training, say, 6 months before you took a break. Of course it all depends on how well your training, nutrition and rest is when you come back after the break too.

So it wouldn't really be 'harder' to get your gains back.. but it still wouldn't be easy, you would still have to work hard to get back in shape if you took 3 months off from training completely. It would be important to also keep your nutrition under control while you were on such a long break too.