Often we are attracted to people who have some sort of similarity with us.
Astrologically, this same-sign you have noticed can create some degree of attraction. BUT notice that these girls are ALL ex-girlfriends. There was attraction, but not enough to stick it out together.
(understand that often the problems don't appear until after the "newness" has worn off .. and THAT is when you start to see if the relationship might last long-term).
In astrology, often one person has their Ascendant or Descendant conjunct (allow an 8-degree orb) the other person's Sun or Moon or Venus or Mars. Without this type of synastry aspect between the two birthcharts, the relationship is either not likely to become a significant relationship or it is not likely to lead to marriage.
Yes, Venus conjunct the other person's Mars is strong sexual attraction. Moon-Mars too, and to some extent Sun-Mars.
Venus in the same sign (but NOT in a conjunct aspect) as the other person's Mars is some sexual attraction.
But note that the experts say that while sexual chemistry is a motivator, it is only 11% of what MAKES a relationship worki/last.
So .. these girls ... some sexual attraction. By itself, this sign-comparison is not going to make it work though. You would need to look at ALL of the synastry aspects between his and her birthchart. And that means having an accurate birthtime for both people, since a birthtime that is even just 4 minutes off might mean the difference between that Ascendant contact or it not being there.
Which means no birhttimes rounded off to the nearest hour or half-hour or even quarter-hour. Astrology absolutely relies on precision, because the less precision you have, the less the chart IS that person's birthchart.