It could be that 10 of Swords is them having a deepening negative feeling they feel about the disposition of the relationship relative to where they are in life currently.
9 of Swords precedes, so 10 of Swords may be the worries coming to light in the waking world (not just your mind's eye) rather than just hanging on top, controlling the individual's attention....
It's possible the relationship itself doesn't look like it can form the right foundation. The other party may be overly optimistic and this may clash with this individual's skeptical viewport of life. Or other red flags pointing to there not being a long-term potential. The foundation may not be based on firm ideas either, maybe too much talk about soul mates, astrological connections, marriage talk, and other floaty floaty stuff that the querent doesn't quite understand and is left scratching their head (10S). They're struggling to see it as the real deal. It may be too pushy and for some this is a quick way to push them away... because they feel they will become a martyr to this version's interpretation of the relationship. Whereas they feel that thinking is over the top and could lead to the other side becoming hurt if they were to pull back.
Another take,
If either or BOTH are going through a healing period, i.e. dealing with major psych issues, self-esteem issues or boundary issues as they are repairing from a major relationship breakup (like marriage) or otherwise are working on themselves to make sure they don't re-engage yet again in unhealthy relationship patterns... then it's possible the feeling is related to it being an impediment in their emotional recovery. That the thoughts and anxieties of the 9 of Sword have went overboard and crushed their willpower to go further on their journey... so they may still be reeling from negative cycles of the prior relationship.
I get this sometimes for people who are working on self-improvement or dealing with anxiety issues after busted up affairs and the relationship is like a "bad" high. That is, it feels great to them and looks good on the surface... but it's going to lead back to a lot of the same roads they've crossed before. It may be they can't stomach it, that it will light a fire back on their old trust issues and cause them to relapse in recovery, i.e. continue negative patterns such as codependency or jealousy problems from the prior union.
It's likely not the fault of the other party in that situation. This person may still living in a negative cycle of thinking, or otherwise recovering psychologically, and they may not yet have the tools yet to get out of 10S thinking. The old behavior patterns are still there and it may affect their self-esteem and sense of self worth to go back this direction. This leaves the person feeling quite mired in their internal melodrama as they really have no reason to feel this distrust of this individual, but yet the trauma from the past are still there, plaguing the querent... could be they don't know how to have a healthier relationship yet, hence the exasperated 10S appearing. They wish they could just move past automatically... therefore still feeling "pulled down" by the prior relationship.
If this comes to light, then it's possible the partner (the non-10S one) can ask to join in on therapy process and make it a safe environment so that the partner can eventually "catch up". However, they would need to reel back their expectations of the relationship a great deal and try to focus on building a firm relationship based on mutual trust and healthy boundaries. If they're seeing a therapist, then it's possible the new partner could join in on the process. Though in some ways, it would be like teaching someone to walk again.
On the other hand, if it is positively dignified, then it's possible they have finally become liberated from these experiences... that they are ready to release the past and move on. Entirely depends on the context of the other cards in the spread. If it's a single card, I would take it at face value.
Other other possibility is that the querent is engaging in shady behavior in the background and they know they've already screwed it up before they even started.
BTW, Page of Cups can indicate the 10S is based in immaturity issues. Whichever partner.