Please help me with the following two phrases! :)
ごめんなさい　/　ごめん　& 申し訳ない /　申し訳
Can someone please clarify if there's a difference between the two phrases; both the ones between the / and &, and if so please explain the difference and what situations to use them in :) Thanks! XD

Question

Please help me with the following two phrases! :) 
ごめんなさい　/　ごめん　&    申し訳ない /　申し訳
Can someone please clarify if there's a difference between the two phrases; both the ones between the / and &, and if so please explain the difference and what situations to use them in :) Thanks! XD

Answer

1．申し訳ありません 
2. ごめんなさい 
3．申し訳ない 
4．ごめん 

I WOULD SAY 
storonger 1 > 2 > 3 > 4 > weaker 

It's not a poker game(black-spadess are storonger than red-hearts) but I would say 申し訳ございません is the strongest apology in these 4, and ごめん is the weakest. 

Also I think there is a particular rule of using them. 
- 申し訳xxxxx is formal. it's more used in a public situation. 
If you apologize to your boss, use this one. 
- ごめんxxxx is more used in a daily/cusual situation. 
When you apologize to your girl firend, you would use this type of apology. 

Again, 
申し訳xxx = for your boss, customer, girl firend's parents or other public situation 
ごめんxxx = for your friends, pairents(most of the time), girl firend, or any cusual situation 
わりぃ・悪い=for your firends, extremely(too) cusual, better use it only to your very close friends. or better not use it. 

Also "すみません" could be substituted to "申し訳ｘｘｘ", but "すみません" is even weaker than "申し訳ｘｘｘｘ".
So if you hear someone says "申し訳ありません” to you, the person is apologizing you really deeply.

Answer

ごめんなさい、ごめん、申し訳ない、はどれも同じ意味ですが、相手によって使い分けます。申し訳、はそれだけで使わず、申し訳ありません。と否定文として使います。
ごめんなさい(話し言葉としてよく使われます。だいたいこれでいいと思います)
すみません(これもよく使われます。とても使い勝手がいいです)
ごめん(年下の人や仲の良い人に対しては、これでいいです)
申し訳ありません(礼儀正しく言いたいときに使います。仲の良い人には、"本当にごめんなさい"でもいいです)ね)
申し訳ない(口語ではそのまま使うより、"申し訳ないと思っています"という使い方が多いですね。)

I hope this may help you.