When you are in any type of relationship with same sun sign, your own qualities and flaws will Magnify. All the positive personality and character traits in both of you will increase in their intensity as well as the negative traits.
You should make efforts to encourage good qualities and minimize bad qualities of each other.
But if other planets between the two horoscopes especially the moon (moon denotes your inner feelings) and the ascendants are having good relations is an intense than Devotion, loyalty and respect will be there between both of you. If ascendants and moon of two horoscopes are in unfavorable axis than your relationships will be tense and difficult indeed.
So just checking your Compatibilities by only sun sign pattern is not full-proof system of match making. So it is better to get your horoscope matched by a qualified astrologer.