The problem was that in the store they had like 6-8 like this one in the same tank and all of them were peaceful so we thought it was a female, also when we were at home we saw a little white bulb, simillat in position to an ovopositor. All Noob mistakes...
Anyway we will care for him and if necesary we will get another tank
I mean we have 3 tanks, one with a male betta another with a female and another without bettas (only some endler's) so we can use a divider or rearrange the endler tank.
The fish welfare it's top priority for us